A comparison of airway responsiveness in smokers with chronic bronchitis and in asthmatic subjects.

Fifty-two of 95 smokers with a forced expiratory volume in one second (FEV1) above 70% predicted and with chronic bronchitis were found to have increased bronchial responsiveness, expressed as PC20FEV1, upon challenge with inhaled histamine. The degree of responsiveness was significantly below that found in matched asthmatics, but substantially higher than that reported in normals. The degree of responsiveness was significantly correlated to prechallenge ventilatory capacity, age and tobacco consumption but not to sex. PC40MEF50 showed the same distribution as PC20FEV1, but did not add further information. The slope of the dose response curve expressing the maximum expiratory flow at 50% of vital capacity expired (MEF50) did not correlate with any of the parameters measured. The slope of the FEV1 dose-response curves showed significant correlation with tobacco consumption. The degree of bronchial responsiveness as an indication for future disability needs to be investigated.